Taxonomic Hierarchy

Introduction

The term Taxonomy was coined by Augustin Pyramus de Candolle. Taxonomy is the science of classification of organisms. Classification of organisms is done by Biologists based on evolutionary relationships and shared features among the organisms.

The fundamental unit of life on Earth is refers to as the species. The species is a population or series of populations whose members are able to interbreed freely under natural conditions and who do not breed with other species.

Closely related species are grouped as genus (pl. genera); while closely related genera are grouped as family and so on. This type of grouping makes up the classification hierarchy. The genus and species names are always either italicized or underlined, with the genus name Capitalized and the species name in lower case.

Species are grouped into more comprehensive taxa, these taxa are grouped into larger taxa so that the classification is a hierarchy of a system of units that increase from first level to the next higher level.

Taxonomic hierarchy

Taxonomic Hierarchy or Linnaean hierarchy categories are introduced by Linnaeus. It is defined as arrangement of categories in a decreasing or increasing order from kingdom level to species level and vice versa. Kingdom is the highest rank given in the hierarchy then the levels division, class, order, family, genus and species follow. Species is the lowest rank given in the Hierarchy.

The hierarchy has two categories namely, obligate (main) and intermediate (intra).

Ø  In obligate category, hierarchy is followed strictly. Here the levels range from kingdom to species.

Ø  In intermediate category, hierarchy is not followed strictly. The levels are added in between the list such as sub-division, super-family, super-class, sub-order, sub-species and so on.

The following are seven main or obligate categories used in any plan of classification. They are known as the supra-specific groups.

1. Kingdom

      2. Division

            3. Class

                 4. Order

                     5. Family

                           6. Genus

                                 7. Species

v Species: 

Group of organisms which are similar in form, shape and reproductive features are called species.  This similarity is important so as to produce fertile offsprings. Offsprings are sterile when a hybrid is produced. The level species is followed by subspecies, clines and demes. These categories are inferior when compared to species.

v Genus:

Genus is a group of related species. Some genera may have only one species (Monotypic) whereas some may have more than one species (polytypic).

v Family: 

Family is the collection of related genera.

v Order:

One or more than one related families form an order.

v Class:

One or more than one related orders form a class.

v Division: 

Division is the term used for plants while its synonym phylum is used for animals. It is a collection of related classes.

v Kingdom: 

Kingdom is the uppermost taxonomic category. For example all the plants are included in Kingdom Plantae. Taxon is the unit of classification that denotes group of organisms based on observable features.

Under species we have other groups termed as infra specific groups. The following is the list of intermediate or infra specific groups,

       1. Species

            2. Subspecies

                   3. Clines

                        4. Demes

Various methods used to recognize and categorize organisms are called as Taxonomic aids. Identification of organisms is a tiresome process. Taxonomic keys are used for identification of organisms. Taxonomic key is a long table of statements with different features to recognize the organisms. The features which are related to a particular organism are chosen and then the organism is grouped into the relevant category.